Q -I've heard about full-color saturation of color slides. Can this same effect apply to prints? If so, how should I change my ASA?

A - Fall saturation in color slides simply means you underexpose slightly, usually within a half stop. You can get the same effect by upping the ASA by half - for example ASA 25 to ASA 32, plus or minus. The reason I say plus or minus is that you'll have to make your own tests since equipment and tastes differ. The reason pros go for full-color saturation is that for good reproductions you have to have detail in the highlight part of the transparency.

Color prints are a different problem, because the saturation (exposure) is added when the print is made. An automatic printer won't adjust to underexpose since it's set for an average. This is what the big labs use. To control the density, you have to have a custom-made point, or make it yourself. Actually, "full-color saturation" is one of those catch phrases that make one sound knowledgeable. The best thing to do is to shoot the best exposure you can. You can call that "full-color saturation" and no one will really know the difference.

Q - Which class of color film would be the best one to use?

A - Color film is like wine: It must age to its proper maturity. And, as in wines, there are two classes: regular film, the vin ordinaire, and professional film, the vintage of chateau variety. The regular emulsions are designed to suit the needs of the photographer who leaves his film in the camera between shooting sessions and doesn't really care whether the color fidelity is absolute, as long as it looks good to the eye. To meet his needs the film is designed for long shelf-life stability of the latent (exposed) image in the camera between takes. It is also higher in contrasts, to compensate for poorer optics and dirty lenses.

Professional film is held to higher standards but requires more care. The ASA is indicated for each individual roll. It is also lower in contrast for better reproduction. The aim point or color fidelity is also held to tighter specifications. When you buy this film, you must use it soon or store it in the refrigerator.

Q -Can you explain the zone system in your column?

A - The zone system is a means of reproducing exact tones through controlled exposure and negative development. It was invented by Ansel Adams, and if you're really interested you should look up his books on the subject. If you're interested in just getting good pictures, you can do it without the zone system by careful chouce of metering.

The basic problem is to decide how to accommodate the greatest range of tone values within the limited range. For example, if you're shooting a snow or beach scene, you want to get detail in your light areas, so you expose for them. But your dark areas will loose detail and go black, relatively speaking.

The opposite is true when you have a dark subject in which you want detail against a light background. By exposing for the dark areas your light background will go whiter. Backlit subjects are a good example.

How much more you cover on either side of the main tone values of your subject depends on how good your technique is as a photographer. Kodak syas: Use an 18 per cent gray card. That's fine for technical photography, but I haven't seen any prize-winning pictures of gray cards lately. Ansel Adams says: Control your technique all the way from the exposure through development and make your own prints. That's fine, but we're not all great technicians who want to do the entire process ourselves.

So use common sense. Decide what is the most important part of your picture.

Then expose for your decision.